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21 * @brief functions related to load calculations
22 * @author Christian Grothoff
25 #include "gnunet_util_lib.h"
28 #define LOG(kind,...) GNUNET_log_from (kind, "util-load", __VA_ARGS__)
31 * Values we track for load calculations.
33 struct GNUNET_LOAD_Value
37 * How fast should the load decline if no values are added?
39 struct GNUNET_TIME_Relative autodecline;
42 * Last time this load value was updated by an event.
44 struct GNUNET_TIME_Absolute last_update;
47 * Sum of all datastore delays ever observed (in ms). Note that
48 * delays above 64k ms are excluded (to avoid overflow within
49 * first 4 billion requests).
51 uint64_t cummulative_delay;
54 * Sum of squares of all datastore delays ever observed (in ms). Note that
55 * delays above 64k ms are excluded (to avoid overflow within
56 * first 4 billion requests).
58 uint64_t cummulative_squared_delay;
61 * Total number of requests included in the cummulative datastore delay values.
63 uint64_t cummulative_request_count;
66 * Current running average datastore delay. Its relation to the
67 * average datastore delay and it std. dev. (as calcualted from the
68 * cummulative values) tells us our current load.
73 * How high is the load? 0 for below average, otherwise
74 * the number of std. devs we are above average, or 100 if the
75 * load is so high that we currently cannot calculate it.
83 internal_update (struct GNUNET_LOAD_Value *load)
85 struct GNUNET_TIME_Relative delta;
88 if (load->autodecline.rel_value_us == GNUNET_TIME_UNIT_FOREVER_REL.rel_value_us)
90 delta = GNUNET_TIME_absolute_get_duration (load->last_update);
91 if (delta.rel_value_us < load->autodecline.rel_value_us)
93 if (0 == load->autodecline.rel_value_us)
95 load->runavg_delay = 0.0;
99 n = delta.rel_value_us / load->autodecline.rel_value_us;
102 load->runavg_delay = 0.0;
109 load->runavg_delay = (load->runavg_delay * 7.0) / 8.0;
115 * Create a new load value.
117 * @param autodecline speed at which this value should automatically
118 * decline in the absence of external events; at the given
119 * frequency, 0-load values will be added to the load
120 * @return the new load value
122 struct GNUNET_LOAD_Value *
123 GNUNET_LOAD_value_init (struct GNUNET_TIME_Relative autodecline)
125 struct GNUNET_LOAD_Value *ret;
127 ret = GNUNET_new (struct GNUNET_LOAD_Value);
128 ret->autodecline = autodecline;
129 ret->last_update = GNUNET_TIME_absolute_get ();
135 * Change the value by which the load automatically declines.
137 * @param load load to update
138 * @param autodecline frequency of load decline
141 GNUNET_LOAD_value_set_decline (struct GNUNET_LOAD_Value *load,
142 struct GNUNET_TIME_Relative autodecline)
144 internal_update (load);
145 load->autodecline = autodecline;
150 * Recalculate our load value.
152 * @param load load to update
155 calculate_load (struct GNUNET_LOAD_Value *load)
163 if (load->cummulative_request_count <= 1)
165 /* calcuate std dev of latency; we have for n values of "i" that:
167 * avg = (sum val_i) / n
168 * stddev = (sum (val_i - avg)^2) / (n-1)
169 * = (sum (val_i^2 - 2 avg val_i + avg^2) / (n-1)
170 * = (sum (val_i^2) - 2 avg sum (val_i) + n * avg^2) / (n-1)
172 sum_val_i = (double) load->cummulative_delay;
173 n = ((double) load->cummulative_request_count);
175 avgdel = sum_val_i / n;
177 (((double) load->cummulative_squared_delay) - 2.0 * avgdel * sum_val_i +
178 n * avgdel * avgdel) / nm1;
180 stddev = 0.01; /* must have been rounding error or zero; prevent division by zero */
181 /* now calculate load based on how far out we are from
182 * std dev; or if we are below average, simply assume load zero */
183 if (load->runavg_delay < avgdel)
186 load->load = (load->runavg_delay - avgdel) / stddev;
191 * Get the current load.
193 * @param load load handle
194 * @return zero for below-average load, otherwise
195 * number of std. devs we are above average;
196 * 100 if the latest updates were so large
197 * that we could not do proper calculations
200 GNUNET_LOAD_get_load (struct GNUNET_LOAD_Value *load)
202 internal_update (load);
203 calculate_load (load);
209 * Get the average value given to update so far.
211 * @param load load handle
212 * @return zero if update was never called
215 GNUNET_LOAD_get_average (struct GNUNET_LOAD_Value *load)
220 internal_update (load);
221 if (load->cummulative_request_count == 0)
223 n = ((double) load->cummulative_request_count);
224 sum_val_i = (double) load->cummulative_delay;
225 return sum_val_i / n;
230 * Update the current load.
232 * @param load to update
233 * @param data latest measurement value (for example, delay)
236 GNUNET_LOAD_update (struct GNUNET_LOAD_Value *load, uint64_t data)
240 internal_update (load);
241 load->last_update = GNUNET_TIME_absolute_get ();
242 if (data > 64 * 1024)
248 dv = (uint32_t) data;
249 load->cummulative_delay += dv;
250 load->cummulative_squared_delay += dv * dv;
251 load->cummulative_request_count++;
252 load->runavg_delay = ((load->runavg_delay * 7.0) + dv) / 8.0;